[PATCH v2] fs: btrfs: fix out of bounds write

[Alex Shumsky]

Fix btrfs_read/read_and_truncate_page write out of bounds of destination
buffer. Old behavior break bootstd malloc'd buffers of exact file size.
Previously this OOB write have not been noticed because distroboot usually
read files into huge static memory areas.

Signed-off-by: Alex Shumsky <alexthreed at gmail.com>
Fixes: e342718 ("fs: btrfs: Implement btrfs_file_read()")
---

Changes in v2:
- fix error path handling
- add Fixes tag
- use min3

 fs/btrfs/inode.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4691612eda..3998ffc2c8 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -640,7 +640,11 @@ static int read_and_truncate_page(struct btrfs_path *path,
 	extent_type = btrfs_file_extent_type(leaf, fi);
 	if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
 		ret = btrfs_read_extent_inline(path, fi, buf);
-		memcpy(dest, buf + page_off, min(page_len, ret));
+		if (ret < 0) {
+			free(buf);
+			return ret;
+		}
+		memcpy(dest, buf + page_off, min3(page_len, ret, len));
 		free(buf);
 		return len;
 	}
@@ -652,7 +656,7 @@ static int read_and_truncate_page(struct btrfs_path *path,
 		free(buf);
 		return ret;
 	}
-	memcpy(dest, buf + page_off, page_len);
+	memcpy(dest, buf + page_off, min(page_len, len));
 	free(buf);
 	return len;
 }
-- 
2.34.1